Vaizdas:Night-Shining Clouds.jpg

Vaizdas iš Vikipedijos, laisvosios enciklopedijos.
Jump to navigation Jump to search
Didesnės raiškos iliustracija(5 184 × 3 456 taškų, rinkmenos dydis: 793 KiB, MIME tipas: image/jpeg)
Commons-logo.svg Ši byla yra iš bendros Wikimedia Commons nemokamų resursų duomenų bazės, palaikomos Wikimedia Foundation organizacijos. Norėdami sužinoti licencijavimo smulkmenas, žiūrėkite paveikslėlio aprašymą
Paveikslėlio aprašymas
Į paveikslėlio aprašymą

Aprašymas[keisti]

Aprašymas
English: After the Sun sets on a summer evening and the sky fades to black, you may be lucky enough to see thin, wavy clouds illuminating the night, such as these seen over Billund, Denmark, on July 15, 2010. Noctilucent or polar mesospheric clouds, form at very high altitudes-between 80 and 85 kilometers (50-53 miles)-which positions them to reflect light long after the Sun has dropped below the horizon. These "night-shining" clouds are rare-rare enough that Matthew DeLand, who has been studying them for 11 years, has only seen them once in person. But the chances of seeing these elusive clouds are increasing.

DeLand, an atmospheric scientist with Science Systems and Applications Inc. and NASA's Goddard Space Flight Center, has found that polar mesospheric clouds are forming more frequently and becoming brighter. He has been observing the clouds in data from Solar Backscatter Ultraviolet instruments that have been flown on satellites since 1978. The graph above shows how the brightness of the clouds has changed in the Northern Hemisphere. For reasons no one fully understands, the brightness wiggles up and down in step with solar activity, with fewer clouds forming when the Sun is most active. The biggest variability is in the far north. Underlying the changes caused by the Sun, however, is a trend toward brighter clouds. The upward trend in brightness, says DeLand, reveals subtle changes in the atmosphere that may be linked to greenhouse gases.

Polar mesospheric clouds are extremely sensitive to changes in atmospheric water vapor and temperature. The clouds form only when temperatures drop below -130 degrees Celsius (-200 Fahrenheit), when the scant amount of water high in the atmosphere freezes into ice clouds. This happens most often in far northern and southern latitudes (above 50 degrees) in the summer when, counter-intuitively, the mesosphere is coldest.

Changes in temperature or humidity in the mesosphere make the clouds brighter and more frequent. Colder temperatures allow more water to freeze, while an increase in water vapor allows more ice clouds to form. Increased water vapor also leads to the formation of larger ice particles that reflect more light.

The fact that polar mesospheric clouds are getting brighter suggests that the mesosphere is getting colder and more humid, says DeLand. Increasing greenhouse gases in the atmosphere could account for both phenomena. In the mesosphere, carbon dioxide radiates heat into space, causing cooling. More methane, on the other hand, puts more water vapor into the atmosphere because sunlight breaks methane into water molecules at high altitudes.

So far, it's not clear which factor-water vapor or cooling-is causing polar mesospheric clouds to change. It's likely that both are contributing, says DeLand, but the question is the focus of current research.
Data
Šaltinis https://www.flickr.com/photos/jepaulsen/4885848845/in/photostream/, http://solarsystem.nasa.gov/multimedia/display.cfm?Category=Planets&IM_ID=17005
Autorius Jan Erik Paulsen

Licencija[keisti]

Checked copyright icon.svg This image was originally posted to Flickr by Jan Erik Paulsen at https://www.flickr.com/photos/38088606@N06/4885848845. It was reviewed on by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0.

w:lt:Creative Commons
autoriaus nurodymas
Šiam failui taikoma Creative Commons Attribution 2.0 Generic licencija.
Jūs galite:
  • dalintis – kopijuoti, platinti bei persiųsti šį darbą
  • pri(si)taikyti – adaptuoti darbą
Su šiomis sąlygomis:
  • autoriaus nurodymas – Privalote nurodyti šio darbo autorių tuo pačiu būdu, kuris buvo nurodytas paties autoriaus ar licencijos suteikėjo (bet ne tokiais būdais, kuriais teigiama, jog jis leido Jums naudoti šį darbą).

Rinkmenos istorija

Paspauskite ant datos/laiko, kad pamatytumėte rinkmeną tokią, kokia ji buvo tuo metu.

Data/LaikasMiniatiūraMatmenysNaudotojasPaaiškinimas
dabartinis23:49, 3 lapkričio 2013Versijos 23:49, 3 lapkričio 2013 miniatiūra5 184 × 3 456 (793 KiB)Stas1995User created page with UploadWizard

Paveikslėlis yra naudojamas šiuose puslapiuose:

Meta duomenys